Don't enforce palette conversion when writing GD images

The GD image format is able to handle truecolor images as of libgd 2.0.12
(<https://github.com/libgd/libgd/blob/gd-2.2.3/src/gd_gd

Don't enforce palette conversion when writing GD images

The GD image format is able to handle truecolor images as of libgd 2.0.12
(<https://github.com/libgd/libgd/blob/gd-2.2.3/src/gd_gd.c#L31-L33>).
Therefore we don't need the potentially lossy and time consuming palette
conversion.

This way, imagegd() can also be used to export raw truecolor image data.

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Implemented Bug #68776 mail() does not have mail header injection prevention for additional headers
(PR 2060)

Fix #72430: [] operator not supported for strings

Remove effectless --enable-gd-native-ttf and USE_GD_IMGSTRTTF

--enable-gd-native-ttf did set USE_GD_IMGSTRTTF, which is otherwise unused
as of commit 8a90aad3 (i.e. PHP 5.5.0), at least.

Update UPGRADING wrt. [RFC]: Add Argon2 to password_*

Merge branch 'pull-request/2115' into PHP-7.1

Added array parameter support to mb_convert_encoding()

Update UPGRADING wrt. commit c4fe264b

Update UPGRADING wrt. RFC: Implement socket_getaddrinfo()

Fix typo in UPGRADING

Allow array input for mb_check_encoding()

Fix some grammatical errors in PHP 7.1 Upgrade Notes

[skip ci]

Revert "Update UPGRADING"

This reverts commit 567f19dd89235ebd7c235939b8d57cb122778f76.

Update NEWS and UPGRADING

Update UPGRADING

Update UPGRADING

Remove accidental NEWS and UPGRADING entries

Merge mistake from PHP-7.1.

Revert "Do not prepend ? on nullables in ReflectionType::__toString()"

This reverts commit 8855a2ce76e8bfba1d2eea1345c765fde7a9a441.

Merge branch 'PHP-7.1'

# Conflicts:
# NEWS
# UPGRADING

Do not prepend ? on nullables in ReflectionType::__toString()

Better BC with 7.0.

Updated UPGRADING about function call args

Return true for is_object() on Incomplete_Class

gettype(): Use "resource (closed)" instead of "unknown type"

Scrub UPGRADING and UPGRADING.INTERNALS

There were already some master-only entries in there -- I hope I
didn't remove anything that was supposed to be there.

[skip ci]

update UPGRADING